1. Field of the Invention
The present invention relates to a composite material for a metal gasket, which is suitably used for an internal combustion engine, such as an automobile engine.
2. Description of the Related Art
In the case of the internal combustion engine such as an automobile engine, for example as shown in FIG. 3, joined surfaces 2a and 3a of flanges 2 and 3 fastened by a bolt 1 or the like are set in a fretting state, where horizontal shifting (horizontal direction fretting) like that indicated by an arrow A in FIG. 4(a) or fretting like that indicated by an arrow C caused by opening like that indicated by an arrow B in FIG. 4(b) repeatedly occurs because of vibration, thermal expansion or the like.
As a result, an inconvenient situation occurs. Specifically, as shown in FIG. 3, when a metal gasket 5 is used between the joined surfaces 2a and 3a of the flanges 2 and 3 for sealing fluids in a fluid passage 4, between the joined surfaces 2a and 3a of the flanges 2 and 3 and a bead portion 5a of the metal gasket 5, friction repeatedly occurs particularly at a projected portion D shown in each of FIGS. 4(a) and 4(b). As shown in FIG. 5, a rubber layer 5c fixed on a metal plate 5b of the metal gasket 5 was worn or peeled off early at the projected portion D, causing a great reduction in sealing performance.
Thus, in an effort to solve the problem of such fretting wear, the following measures have conventionally been tried:
(a) a frictional force generated by fretting is reduced by coating solid lubricant (graphite, molybdenum disulfide or the like) containing inorganic powder on the surface of the fixed rubber layer;
(b) a frictional force generated by fretting is reduced by coating liquid lubricant (wax, oil, fatty acid or the like) on the surface of the fixed rubber layer;
(c) wear resistance is enhanced by increasing the curing degree of the fixed rubber layer, or the addition amount of carbon black or a filler component in a rubber composition so as to increase the hardness of the fixed rubber layer; and
(d) as disclosed in Japanese Utility Model Laid-Open H2 (1990)-59362, and Japanese Utility Model Laid-Open H3 (1991)-124075, a metal gasket is slid to either one of the two joined surfaces sandwiching the metal gasket by providing a difference in frictional resistance between the front and back sides of the metal gasket.
However, there have been problems inherent in the foregoing measures. Specifically, in the case of the measure (a), the effect of reducing a frictional force by the lubricant containing inorganic powder is low, and the effect of reducing a frictional force cannot be obtained before the adaptation (transfer) of the solid lubricant to the flange joined surfaces. Consequently, the fixed rubber layer is worn when high-load fretting occurs in an initial state. In the case of the measure (b), the liquid lubricant is deteriorated with time if a use environment temperature of the metal gasket is severe, losing the effect of reducing a frictional force. Besides, depending on fluids to be sealed, the liquid lubricant is eluted by the fluids and lost, similarly increasing a frictional force to wear the fixed rubber layer.
In the case of the measure (c), the increased hardness of the fixed rubber layer causes reductions in sealing performances in a low surface pressure region and in a rough surface, resulting in the loss of the original sealing function of the metal gasket. In the case of the measure (d), since the wear of the fixed rubber layer caused by fretting is absorbed only by one side of the gasket, the degree of reduction in sealing performance is reduced. However, the problem still remains to be solved because the wear of the rubber layer is not eliminated completely. In addition, if a portion (high-pressure sealing portion, a fuel sealing portion or the like) requiring high sealing performance is present in the surface of a side, in which fretting occurs, this measure cannot be selected.
It is an object of the present invention to provide a composite material for a metal gasket, which is capable of advantageously solving the foregoing problems. In accordance with a first aspect of the present invention, a composite material for a metal gasket is provided, including: a metal plate; a rubber layer fixed on a surface of the metal plate; and a solid lubricant layer fixed on the rubber layer. The solid lubricant layer contains polytetrafluoroethylene and a resin as main components, and has a friction coefficient equal to 0.15 or lower.
In the metal gasket using the composite material of the present invention, since the solid lubricant layer fixed on the rubber layer contains polytetrafluoroethylene (PTFE) having a low friction coefficient, a high heat resistance and a stable chemical property, and a resin such as a synthetic resin or the like, the resin serves as a curing agent to fix PTFE on the rubber layer, and the PTFE reduces the friction coefficient of the solid lubricant layer to a low value of 0.15 or lower, thereby greatly reducing a frictional force between the metal gasket and joined surfaces.
According to the composite material of a first aspect of the present invention, the occurrence of wear in the fixed rubber layer can be effectively prevented even when high-load fretting occurs in an initial state. In addition, the loss of a fictional force reducing effect caused by deterioration with time can be prevented even when the environmental temperature of using the metal gasket is severe, and the loss of the lubricant caused by elution into fluids to be sealed can be prevented. As a result, it is possible to obtain sealing performance always stable for a long time.
Further, according to the composite material of the first aspect of the present invention, since wear can be prevented without any particular increase in hardness of the fixed rubber layer, no reductions occur in the sealing performance of a low surface pressure region, and the sealing performance of a rough surface. As a result, the original sealing function of the metal gasket can be maintained. Moreover, since the wear of the fixed rubber layer caused by fretting can be prevented in both sides of the gasket, even when a portion (a high-pressure sealing portion, a fuel sealing portion or the like) requiring high sealing performance exists in the surface of a fretting occurrence side, it is possible to sufficiently meet the requirement.
In accordance with a second aspect of the invention, a composite material for a metal gasket is provided, including: a metal plate; a rubber layer fixed on a surface of the metal plate; and a solid lubricant layer fixed on the rubber layer. The solid lubricant layer contains polytetrafluoroethylene, a resin and carbon black as main components, and has a friction coefficient equal to 0.15 or lower.
According to the composite material of the second aspect of the present invention, an operation and effect similar to that of the composite material of the first aspect can be obtained, and the carbon black functions as a releasing agent. Thus, it is possible to prevent the occurrence of blocking (phenomenon of adhering of layers fixed on metal plates to each other) when the composite material is stored in a stacked manner.
In the composite material of the invention, preferably, carbon black of 1 to 10 wt % (i.e. not less than 1 wt % and not more than 10 wt %) is contained in the solid lubricant layer. If the content of carbon black is less than 1 wt %, a sufficient releasing operation is not provided. On the other hand, if the content of carbon black exceeds 10 wt %, the friction coefficient of the solid lubricant layer becomes excessively large.